1. Field of the Invention
The present invention provides a process for producing resin for a toner, which resin has an excellent offset resistance and fixing property.
2. Description of the Background
Many proposals have been made regarding dry type toner resins. However, in view of the need for an increased information processing rate, it has become very desirable for copying machines and recording apparatus to have increased copying speeds.
Additionally, in order to conserve energy, there is also presently a need for a toner which can be fixed at lower temperatures than at present.
On the other hand, the melting viscosity of a resin is reduced if the fixing property of the toner at a lower temperature is improved. This results in easy deposition of the toner to a fixing roll and worsening of offset resistance. One method for resolving this problem has been proposed wherein a resin having a wide molecular weight distribution is used for the toner. For example, there can be mentioned a method of preparing a high molecular weight polymer and a low molecular weight polymer separately by solution polymerization and, subsequently, mixing the polymers in the liquid state and then removing the solvent. Unfortunately, it is difficult to produce a high molecular weight polymer with a weight average molecular weight of higher than 200,000 using the solution polymerization process. Further, since the solvents used for the high molecular weight polymer and those for the low molecular weight polymer differ greatly, uniform mixing of the two kinds of the polymers is difficult even when in solution. In addition, the above technique requires the removal of solvent which is troublesome and increases cost.
Further, even by the suspension polymerization process which is advantageous in view of the cost, it is difficult to produce high molecular weight polymers with a molecular weight of higher than 200,000. Moreover, polymers having a sufficiently wide molecular weight distribution are as yet unobtainable.
Emulsion polymerization has been used to obtain high molecular weight polymers, however, since emulsifier remains in the resin formed, the moisture resistance and fluidity of the toner are reduced and/or special liquid waste processing is necessary because of high biological oxygen demand (BOD) in liquid wastes therefrom.
Thus, a need continues to exist for a process for producing a uniform resin for toner having a wide molecular weight distribution which avoids the problems associated with the conventional methods used for preparing toner resin.